Kennedy took the podium at the Democratic convention in his Boston stronghold on Tuesday to herald his junior Senate colleague as the country's saviour after four years of Republican rule.
"Our struggle is with the politics of fear and favouritism in our own time, in our own country," he told 5000 delegates. "Our struggle is with those who put their own narrow interest ahead of the public interest."
Making a passionate plea for traditional Democratic values protecting the poor and the afflicted, Kennedy drew a sharp contrast between his party and a Bush administration he said had burned its bridges with the rest of the world.
"Interdependence defines our world. For all our might, for all our wealth, we know we are only as strong as the bonds we share with others," he told the crowd.
"America needs a genuine uniter," he said. "And John Kerry has the skill and the judgment and the experience to lead us on that great journey."
The two men have known each other since 1971 when Kerry, a decorated Vietnam veteran, travelled to Washington to join protests against the war.
"I am personally convinced that if John Kerry was president of the United States during that time we never would have had an Iraq war. We never would have gone to war"
Senator Edward Kennedy
"I saw right into his soul, saw the inner angst, the suffering that he had experienced, the sense of loss that he had seen, and the passion that he had in terms of a failed and mistaken national policy," Kennedy said.
"I'm a very strong believer in John Kerry. And I think the people will make a judgment at the time he announces. They'll make a judgment on Thursday night when they see him."
Nevertheless, there have been tensions between the two over the years.
Kerry has often had to live in the shadow of his illustrious Massachusetts partner, who has been in the Senate for nearly 42 years. But they have built up strong links.
Kennedy has for months been speaking out for Kerry, defending the Democratic candidate's vote in Congress for the Iraq invasion when he had voted against.
Kennedy twice tried to seek the
party's presidential nomination
"I am personally convinced that if John Kerry was president of the United States during that time we never would have had an Iraq war. We never would have gone to war," Kennedy said on Sunday.
Now Kerry is at centre stage in the convention which is being held in the New England home of the legendary Kennedy family.
Many people believe it may be the last great national battle fought by Kennedy.
He has twice run for the presidential nomination to take up the mantle of his assassinated brothers John and Robert. But he says there is no bitterness about seeing Kerry overtake him.
"My pursuit is public service, not the constant pursuit of the presidency," Kennedy insisted.
Kerry is running neck and neck
with the president in opinion polls
"I said that almost 25 years ago. So I've been honoured to serve in the United States Senate. I love the United States Senate. And we've been able to get a number of things done in the United States Senate."
To many conservatives, Kennedy is the archetypal northern left-winger. The death of a female campaign aide in a controversial car accident in July 1969 tarnished his reputation and all but killed his White House hopes.
But Kennedy is also seen as the incarnation of the power of the Democratic party and its conscience.
"He's the patriarch of the party, the good old man who has a lot of influence and who's respected among Republicans here," said Denton Crews who was at university with Kennedy.
"He has stood for liberal positions nobody would have stood for, on health care, education, he's very effective on the floor of the Senate, he always had the very best staff, he speaks out on issues and when he does he's listened," added Crews.
"Our struggle is with the politics of fear and favouritism in our own time, in our own country. Our struggle is with those who put their own narrow interest ahead of the public interest"
Senator Edward Kennedy
"He would have made a good president, but maybe he was too young then."
Kennedy's four decades in the Senate make him the third longest serving member of the body. But he shows no sign of stepping down and says he will stand again in 2006.
"I intend to stay in this job until I get the hang of it," he told the convention.